Can′t activate MailPoet

Hi,
i′m working on a relaunch of a website. I′m using MAMP with PHP 7 and WP 4.7.1 .
After install, when i try to activate, i got a message like: “Safari can′t open page because server closed connection. This could happen because server is overloaded.”
The original message is in German.
I tried to install directly from www.ads-software.com, download to my computer and install and copy via ftp and activate. Doesn′t matter what i try, i′m getting the same message all the time.
I deactivated all other plugins and tried to activate MailPoet – same result.
I desperately need MailPoet for this Website. It is working with the same theme and all other plugins on the actual Live-Site. The only plugin that is new is “WP Media folder”, but as i mentioned before, even when i deactivate all other plugins, it doesn’t work.
Is anyone out there with an idea of what can cause this error?

What can i do?